In this case, I think it is reasonable to demand that a white guy, a black guy, and a female all receive same wages. But the situation where a black guy is hired by a rich and powerful boss, so nobody dares questioning his wages for the fear of his boss, and so everyone should pretend to only discuss an isolated question (woman's wages), is untenable.
Selective application of a principle (or a law) to some, may be considered as a form of oppression, like in the US, when white guys caught with a small amount of marijuana get sent home, but black guys with the same amount get sent to prison; or in Russia, where the laws are extremely strict, but are rarely applied to rich or powerful or well-connected.
